The inventive concepts provided herein relate to an image sensor, and more particularly, to an image sensor having a test circuit for controlling a test operation for a counter used for analog-to-digital conversion.
An image sensor includes an analog-to-digital converter (ADC) for converting an image signal detected as an analog signal into a digital signal. A pixel array of the image sensor includes a plurality of pixels arranged in a 2D matrix, and each of the pixels outputs an image signal from light energy. Each of the pixels integrates a light charge corresponding to the amount of light incident through a photodiode and outputs a pixel signal of an analog signal according to the integrated light charge. The pixel signal is converted into a digital signal by the ADC.
The ADC includes a comparator for comparing an image signal corresponding to each column of the pixel array with a ramp signal and a counter for performing a counting operation according to the comparison result of the comparator to generate a counting result value or a counting code. The counting code of the counter is output as a pixel signal of the digital signal in response to a column selection signal of a column decoder, and is finally output as image data to an outside of the output buffer. In order to realize clear image data, it is important to detect errors in the column decoder, the counter, and a timing controller.